Thermodynamic Inhibition of Microbial Sulfur Disproportionation in a Multisubunit Designed Sulfur-Siderite Packed Bioreactor.

Sulfur disproportionation (S0DP) poses a challenge to the robust application of sulfur autotrophic denitrification due to unpredictable sulfide production, which risks the safety of downstream ecosystems. This study explored the S0DP occurrence boundaries with nitrate loading and temperature effects. The boundary values increased with the increase in temperature, exhibiting below 0.15 and 0.53 kg-N/m3/d of nitrate loading at 20 and 30 °C, respectively. A pilot-scale sulfur-siderite packed bioreactor (150 m3/d treatment capacity) was optimally designed with multiple subunits to dynamically distribute the loading of sulfur-heterologous electron acceptors. Operating two active and one standby subunit achieved an effective denitrification rate of 0.31 kg-N/m3/d at 20 °C. For the standby subunit, involving oxygen by aeration effectively transformed the facultative S0DP functional community from S0DP metabolism to aerobic respiration, but with enormous sulfur consumption resulting in ongoing sulfate production of over 3000 mg/L. Meanwhile, acidification by the sulfur oxidation process could reduce the pH to as low as 2.5, which evaluated the Gibbs free energy (ΔG) of the S0DP reaction to +2.56 kJ, thermodynamically suppressing the S0DP occurrence. Therefore, a multisubunit design along with S0DP inhibition strategies of short-term aeration and long-term acidification is suggested for managing S0DP in various practical sulfur-packed bioreactors.

H*ads dynamics engineering via bimetallic Pd-Cu@MXene catalyst for enhanced electrocatalytic hydrodechlorination.

Electrocatalytic hydrodechlorination (EHDC) is a promising approach to safely remove halogenated emerging contaminants (HECs) pollutants. However, sluggish production dynamics of adsorbed atomic H (H*ads) limit the applicability of this green process. In this study, bimetallic Pd-Cu@MXene catalysts were synthesized to achieve highly efficient removal of HECs. The alloy electrode (Pd-Cu@MX/CC) exhibited better EHDC performance in comparison to Pd@MX/CC electrode, resulting in diclofenac degradation efficiency of 93.3 ± 0.1%. The characterization analysis revealed that the Pd0/PdII ratio decreased by forming bimetallic Pd-Cu alloy. Density functional theory calculations further demonstrated the electronic configuration modulation of the Pd-Cu@MXene catalysts, optimizing binging energies for H* and thereby facilitating H*ads production and tuning the reduction capability of H*ads. Noteably, the amounts and reduction potential of H*ads for Pd-Cu@MXene catalysts were 1.5 times higher and 0.37 eV lower than those observed for the mono Pd electrode. Hence, the introduction of Cu into the Pd catalyst optimized the dynamics of H*ads production, thereby conferring significant advantages to EHDC reactions. This augmentation was underscored by the successful application of the alloy catalysts supported by MXene in EHDC experiments involving other HECs, which represented a new paradigm for EHDC for efficient recalcitrant pollutant removal by H*ads.

Boosting Hydroxyl Radical Yield via Synergistic Activation of Electrogenerated HOCl/H2O2 in Electro-Fenton-like Degradation of Contaminants under Chloride Conditions.

Hydroxyl radical production via catalytic activation of HOCl is a new type of Fenton-like process. However, metal-chlorocomplex formation under high chloride conditions could deactivate the catalyst and reduce the process efficiency. Herein, in situ electrogenerated HOCl was activated to •OH via a metal-free, B/N-codoped carbon nanofiber cathode for the first time to degrade contaminant under high chloride condition. The results show 98% degradation of rhodamine B (RhB) within 120 min (k = 0.036 min-1) under sulfate conditions, while complete degradation (k = 0.188 min-1) was obtained in only 30 min under chloride conditions. An enhanced degradation mechanism consists of an Adsorb & Shuttle process, wherein adsorption concentrates the pollutants at the cathode surface and they are subsequently oxidized by the large amount of •OH produced via activation of HOCl and H2O2 at the cathode. Density functional theory calculations verify the pyridinic N as the active site for the activation of HOCl and H2O2. The process efficiency was also evaluated by treating tetracycline and bisphenol A as well as high chloride-containing real secondary effluents from a pesticide manufacturing plant. High yields of •OH and HOCl allow continuous regeneration of the cathode for several cycles, limiting its fast deactivation, which is promising for real application.

Complementary Biotransformation of Antimicrobial Triclocarban Obviously Mitigates Nitrous Oxide Emission toward Sustainable Microbial Denitrification.

Sustainable nitrogen cycle is an essential biogeochemical process that ensures ecosystem safety and byproduct greenhouse gas nitrous oxide reduction. Antimicrobials are always co-occurring with anthropogenic reactive nitrogen sources. However, their impacts on the ecological safety of microbial nitrogen cycle remain poorly understood. Here, a denitrifying bacterial strain Paracoccus denitrificans PD1222 was exposed to a widespread broad-spectrum antimicrobial triclocarban (TCC) at environmental concentrations. The denitrification was hindered by TCC at 25 µg L-1 and was completely inhibited once the TCC concentration exceeded 50 µg L-1. Importantly, the accumulation of N2O at 25 µg L-1 of TCC was 813 times as much as the control group without TCC, which attributed to the significantly downregulated expression of nitrous oxide reductase and the genes related to electron transfer, iron, and sulfur metabolism under TCC stress. Interestingly, combining TCC-degrading denitrifying Ochrobactrum sp. TCC-2 with strain PD1222 promoted the denitrification process and mitigated N2O emission by 2 orders of magnitude. We further consolidated the importance of complementary detoxification by introducing a TCC-hydrolyzing amidase gene tccA from strain TCC-2 into strain PD1222, which successfully protected strain PD1222 against the TCC stress. This study highlights an important link between TCC detoxification and sustainable denitrification and suggests a necessity to assess the ecological risks of antimicrobials in the context of climate change and ecosystem safety.

Response of sulfur-metabolizing biofilm to external sulfide in element sulfur-based denitrification packed-bed reactor.

Dosing sulfide into the sulfur-packed-bed (S0PB) has great potential to enhance the denitrification efficiency by providing compensatory electron donors, however, the response of sulfur-metabolizing biofilm to various sulfide dosages has never been investigated. In this study, the S0PB reactor was carried out with increasing sulfide dosages by 3.6 kg/m3/d, presenting a decreasing effluent nitrate from 14.2 to 2.7 mg N/L with accelerated denitrification efficiency (k: 0.04 to 0.27). However, 6.5 mg N/L of nitrite accumulated when the sulfide dosage exceeded 0.9 kg/m3/d (optimum value). The increasing electron export contribution of sulfide a maximum of 85.5% illustrated its competition with the in-situ sulfur. Meanwhile, over-dosing sulfide caused serious biofilm expulsion with significant decreases in the total biomass, live cell population, and ATP by 90.2%, 86.7%, and 54.8%, respectively. This study verified the capacity of dosing sulfide to improve the denitrification efficiency in S0PB but alerted the negative effect of exceeded dosing.

Synergistic between autotrophic and heterotrophic microorganisms for denitrification using bio-S as electron donor.

In recent years, biological sulfur (bio-S) was employed in sulfur autotrophic denitrification (SAD) in which autotrophic Thiobacillus denitrificans and heterotrophic Stenotrophomonas maltophilia played a key role. The growth pattern of T.denitrificans and S.maltophilia exhibited a linear relationship between OD600 and CFU when OD600 < 0.06 and <0.1, respectively. When S.maltophilia has applied alone, the NorBC and NosZ were undetected, and denitrification was incomplete. The DsrA of S.maltophilia could produce sulfide as an alternative electron donor for T.denitrificans. Even though T.denitrificans had complete denitrification genes, its efficiency was low when used alone. The interaction of T.denitrificans and S.maltophilia reduced nitrite accumulation, leading to complete denitrification. A sufficient quantity of S.maltophilia may trigger the autotrophic denitrification activity of T.denitrificans. When the colony-forming units (CFU) ratio of S.maltophilia to T.denitrificans was reached at 2:1, the highest denitrification performance was achieved at 2.56 and 12.59 times higher than applied alone. This research provides a good understanding of the optimal microbial matching for the future application of bio-S.

A critical review on graphene oxide membrane for industrial wastewater treatment.

An important way to promote the environmental industry's goal of carbon reduction is to promote the recycling of resources. Membrane separation technology has unique advantages in resource recovery and advanced treatment of industrial wastewater. However, the great promise of traditional organic membrane is hampered by challenges associated with organic solvent tolerance, lack of oxidation resistance, and serious membrane fouling control. Moreover, the high concentrations of organic matter and inorganic salts in the membrane filtration concentrate also hinder the wider application of the membrane separation technology. The emerging cost-effective graphene oxide (GO)-based membrane with excellent resistance to organic solvents and oxidants, more hydrophilicity, lower membrane fouling, better separation performance has been expected to contribute more in industrial wastewater treatment. Herein, we provide comprehensive insights into the preparation and characteristic of GO membranes, as well as current research status and problems related to its future application in industrial wastewater treatment. Finally, concluding remarks and future perspectives have been deduced and recommended for the GO membrane separation technology application for industrial wastewater treatment, which leads to realizing sustainable wastewater recycling and a nearly "zero discharge" water treatment process.

Thiosulfate as external electron donor accelerating denitrification at low temperature condition in S0-based autotrophic denitrification biofilter.

This study was carried out to determine the inhibition of low temperature on the performance of S0-based autotrophic denitrification (S0-SAD) biofilter, and proposed to enhance the nitrate removal efficiency with thiosulfate as external electron donor. With the decline of temperature from 30 °C to 10 °C at 0.25 h of empty bed contact time (EBCT), the nitrate removal rate presented a logarithmical drop, and the effluent nitrate dramatically increased from 9.19 mg L-1 to 15.13 mg L-1. EBCT was prolonged until 0.33 h for 20 °C, 0.66 h for 15 °C and 1.5 h for 10 °C, respectively, to maintain the effluent nitrate below 10 mg L-1. Such excessive variation of EBCT for different temperature is undoubtedly incredible for practical engineering. Thiosulfate, as the external electron donor, was adopted to compensate the efficiency loss during temperature decrease, which significantly prompted nitrate removal rate to 0.59, 0.53 and 0.31 kg N m-3 d-1 at 20 °C, 15 °C and 10 °C conditions, respectively, even at a short EBCT of 0.25 h. It not only acted as compensatory electron donor for nitrate removal, but also promoted the contribution of elemental sulfur via accelerating the DO consumption and extended larger effective volume of S0-layer for denitrification. Meanwhile, the significant enrichment of Sulfurimonas and Ferritrophicum provided biological evidences to the enhancement process. However, the incomplete consumption of thiosulfate was observed especially at EBCT of 0.25 h and 10 °C, and the thiosulfate runoff needs to be concerned in case of contaminating the effluent. Herein, approximately extending EBCT to 0.66 h and decreasing thiosulfate dosage were conducted simultaneously, thereby achieving 100% thiosulfate utilization efficiency and expected nitrate removal. This study provided a fundamental guidance to design and operate S0-SAD biofilter in response to seasonal temperature variation for practical engineering.

Mitigating nitrite accumulation during S0-based autotrophic denitrification: Balancing nitrate-nitrite reduction rate with thiosulfate as external electron donor.

This study was carried out to determine the effect of influent nitrate loading on nitrite accumulation during elemental-sulfur based denitrification process, and proposed to enhance the nitrogen removal efficiency by mitigating nitrite accumulation with thiosulfate as external electron donor. Along with increasing the nitrate influent loading (from 0.09 kg N/m3/d to 1.73 kg N/m3/d) by shortening the empty bed contact time (EBCT) (from 5 h to 0.25 h), the nitrate removal loading increased from 0.08 to 0.83 kg N/m3/d. Meanwhile, the raise of the nitrate influent loading obviously aggravated the nitrite accumulation. Herein, nitrite began to accumulate since the nitrate influent loading was over 0.86 kg N/m3/d, and a maximum nitrite accumulation of 2.39 mg/L was observed under the 0.25 h of EBCT and 15 mg/L of nitrate influent concentration condition. Thiosulfate was used as the external electron donor to accelerate the nitrite reduction rate in order to mitigate the nitrite accumulation. As a result, the nitrite accumulation significantly decreased from 2.39 mg/L to 0.17 mg/L with the thiosulfate dosage of 13.36 mg/L. However, the nitrite accumulation bounced with the on-going increase of the thiosulfate dosage, indicating that the nitrate reduction rate and nitrite reduction rate were accelerated alternatively. After dosing thiosulfate, the relative abundances of sulfurimonas and ferritrophicum grew up significantly.

Rational design of biogenic PdxAuy nanoparticles with enhanced catalytic performance for electrocatalysis and azo dyes degradation.

The green biogenic PdAu nanoparticles (bio-PdAu NPs) exhibits remarkable catalytic performance in hydrogenation, which is highly desired. However, the catalytic principles and effectiveness of bio-PdxAuy NPs in response to various catalytic systems (electrocatalysis and suspension-catalysis) are unclear. Herein, a facile synthetic strategy for bio-PdxAuy NPs synthesis with controlled size and the catalytic principles for hydrogen evolution reaction (HER) and azo dye degradation is reported. In the biosynthetic process, the size and composition of the bio-PdxAuy NPs could be precisely controlled by predesigning the precursor mass ratio of Pd/Au, and the Au proportion showed a linear relationship with the size of NPs (R2 = 0.92). The obtained bio-PdxAuy NPs exhibit variable activity in electrocatalysis (HER) and suspension-catalysis (azo dye degradation). For electrocatalysis, the formation of conductive networks that facilitates the extracellular electron transfer is crucial. It was revealed that the bio-Pd2Au8 exhibited superior electrocatalytic performance in HER/toward hydrogen evolution, with a maximum current density of 1.65 mA cm-2, which was 1.54 times higher than that commercial Pd/C (1.07 mA cm-2). The high electrocatalytic activity was attributed to its appropriate size (81.38 ± 6.14 nm) and uniform distribution on the cell surface, which promoted the extracellular electron transfer by constructing a conductive network between catalyst and electrode. However, for suspension-catalysis, the size effect and synergistic effect of bimetallic NPs have a more prominent effect on the degradation of azo dyes. As the increase of Au proportion the particle size decreases, and the catalytic activity of bio-PdxAuy improved significantly. The response principles of bio-PdxAuy proposed in this study provide a reliable reference for the rational design of bio-based bimetallic catalysts with enhanced catalytic performance.

Influence on denitrifying community performance by the long-term exposure to sulfamethoxazole and chlortetracycline in the continuous-flow EGSB reactors.

The response of the denitrification community to long-term antibiotic exposure requires further investigation. Here, the significantly altered denitrifying community structure and function were observed by continuous exposure to 1 mg/L sulfamethoxazole (SMZ) or chlortetracycline (CTC) for 180 d in the expanded granular sludge bed reactors. Thaurea, positively correlated with SMZ and NO3- removal efficiency (NrE), was highly enriched in the SMZ-added reactor, while, Comamons and Acinetobacter were largely inhibited. The acute inhibited and then gradual-recovered NrE (87.17-90.38 %) was observed with highly expressed narG, indicating the adaptability of Thaurea to SMZ. However, the abundance of Thaurea and Comamonas greatly decreased, while Melioribacter and Acinetobacter were largely enriched in the CTC-added reactor. CTC created more serious and continuous inhibition of NO3- reduction (NrE of 64.53-66.95 %), with lowly expressed narG. Improved NO2- reduction capacity was observed in both reactors (70.16-95.42 %) with highly expressed nirS and nosZ, revealing the adaptability of NO2- reduction populations to antibiotics.

Candidatus Kaistella beijingensis sp. nov., Isolated from a Municipal Wastewater Treatment Plant, Is Involved in Sludge Foaming.

Biological foaming (or biofoaming) is a frequently occurring problem in wastewater treatment plants (WWTPs) and is attributed to the overwhelming growth of filamentous bulking and foaming bacteria (BFB). Biological foaming has been intensively investigated, with BFB like Microthrix and Skermania having been identified from WWTPs and implicated in foaming. Nevertheless, studies are still needed to improve our understanding of the microbial diversity of WWTP biofoams and how microbial activities contribute to foaming. In this study, sludge foaming at the Qinghe WWTP of China was monitored, and sludge foams were investigated using culture-dependent and culture-independent microbiological methods. The foam microbiomes exhibited high abundances of Skermania, Mycobacterium, Flavobacteriales, and Kaistella. A previously unknown bacterium, Candidatus Kaistella beijingensis, was cultivated from foams, its genome was sequenced, and it was phenotypically characterized. Ca. K. beijingensis exhibits hydrophobic cell surfaces, produces extracellular polymeric substances (EPS), and metabolizes lipids. Ca. K. beijingensis abundances were proportional to EPS levels in foams. Several proteins encoded by the Ca. K. beijingensis genome were identified from EPS that was extracted from sludge foams. Ca. K. beijingensis populations accounted for 4 to 6% of the total bacterial populations in sludge foam samples within the Qinghe WWTP, although their abundances were higher in spring than in other seasons. Cooccurrence analysis indicated that Ca. K. beijingensis was not a core node among the WWTP community network, but its abundances were negatively correlated with those of the well-studied BFB Skermania piniformis among cross-season Qinghe WWTP communities. IMPORTANCE Biological foaming, also known as scumming, is a sludge separation problem that has become the subject of major concern for long-term stable activated sludge operation in decades. Biological foaming was considered induced by foaming bacteria. However, the occurrence and deterioration of foaming in many WWTPs are still not completely understood. Cultivation and characterization of the enriched bacteria in foaming are critical to understand their genetic, physiological, phylogenetic, and ecological traits, as well as to improve the understanding of their relationships with foaming and performance of WWTPs.

Microbial fuel cell-upflow biofilter coupling system for deep denitrification and power recovery: Efficiencies, bacterial succession and interactions.

The excess organic carbon is often added to meet denitrification requirements during municipal wastewater treatment, resulting in the carbon waste and increased risk of secondary pollution. In this study, microbial fuel cell (MFC) was coupled with an up-flow denitrification biofilter (BF), and the long-term performances of denitrification and power output were investigated under the different carbon source concentration. With sodium acetate (NaAc) of 600 mg/L and 300 mg/L, the favorable denitrification efficiencies were obtained (98.60%) and the stable current output was maintained (0.44 mÃ0.48 mA). By supplying NaAc of 150 mg/L, the high denitrification efficiency remained in a high range (89.31%) and the current output maintained at 0.12 mA, while, the denitrification efficiency dropped to 71.34% without coupling MFC. Electron balance analysis indicated that both nitrate removal and electron recovery efficiencies were higher in MFC-BF than that in BF, verifying the improved denitrification and carbon utilization performance. Coupling MFC significantly altered the bacterial community structure and composition, and while, the diversified abundance and distribution of bacterial genera were observed at the different locations. Compared with BF, the more exoelectrogenic genera (Desulfobacterium, Trichococcus) and genera holding both denitrifying and electrogenic functions (Dechloromonas, Geobacter) were found dominated in MFC-BF. Instead, the dominating genera in BF were Dechloromonas, Desulfomicrobium, Acidovorax and etc. By coupling MFC, the more complex and diversified network and the closer interaction relationships between the dominant potential functional genera were found. The study provides a feasible approach to effectively improve the denitrification efficiency and organic carbon recovery for deep denitrification process.

Sulfur autotrophic denitrification filter and heterotrophic denitrification filter: Comparison on denitrification performance, hydrodynamic characteristics and operating cost.

Sulfur autotrophic denitrification (SAD) process, as an alternative to heterotrophic denitrification (HD) filter, receives growing interest in polishing the effluent from secondary sewage treatment. Although individual studies have indicated several advantages of SAD over HD, rare study has compared these two systems under identical condition and by using real secondary effluent. In this study, two small pilot scale filters (SAD and HD) were designed with identical configuration and operated parallelly by feeding the real secondary effluent from a WWTP. The results showed SAD filter can be started up without the addition of soluble electron donor, although the time (14 days) was about 3 times longer than that of HD filter. The nitrate removal rate of SAD filter at HRT of 1.4 h was measured as 0.268 ± 0.047 kg N/(m3∙d). Similar value was observed in HD filter with supplementing 90 mg/L COD. The COD concentration of effluent always kept lower than that of influent in SAD filter but not in HD filter. In addition, SAD filter could maintain a stable denitrification performance without backwash for 15 days, while decline of nitrate removal rate was observed in HD filter just 2 days after stopping the backwash. This different behavior was further confirmed as the SAD filter had a better hydraulic flow pattern. Analysis according to high-throughput 16S rRNA gene-based Illumina MiSeq sequencing clearly showed the microbial community evolution and differentiation among the samples of seed sludge, SAD and HD filters. Finally, the economic assessment was carried out, showing the operation cost of SAD filter was over 50% lower than that of HD filter.

Tropical and temperate wastewater treatment plants assemble different and diverse microbiomes.

The diversity and assembly of activated sludge microbiomes play a key role in the performances of municipal wastewater treatment plants (WWTPs), which are the most widely applied biotechnological process systems. In this study, we investigated the microbiomes of municipal WWTPs in Bangkok, Wuhan, and Beijing that respectively represent tropical, subtropical, and temperate climate regions, and also explored how microbiomes assembled in these municipal WWTPs. Our results showed that the microbiomes from these municipal WWTPs were significantly different. The assembly of microbiomes in municipal WWTPs followed deterministic and stochastic processes governed by geographical location, temperature, and nutrients. We found that both taxonomic and phylogenetic α-diversities of tropical Bangkok municipal WWTPs were the highest and were rich in yet-to-be-identified microbial taxa. Nitrospirae and ß-Proteobacteria were more abundant in tropical municipal WWTPs, but did not result in better removal efficiencies of ammonium and total nitrogen. Overall, these results suggest that tropical and temperate municipal WWTPs harbored diverse and unique microbial resources, and the municipal WWTP microbiomes were assembled with different processes. Implications of these findings for designing and running tropical municipal WWTPs were discussed. KEY POINTS: • Six WWTPs of tropical Thailand and subtropical and temperate China were investigated. • Tropical Bangkok WWTPs had more diverse and yet-to-be-identified microbial taxa. • Microbiome assembly processes were associated with geographical location.

Casimicrobium huifangae gen. nov., sp. nov., a Ubiquitous "Most-Wanted" Core Bacterial Taxon from Municipal Wastewater Treatment Plants.

Microorganisms in wastewater treatment plants (WWTPs) play a key role in the removal of pollutants from municipal and industrial wastewaters. A recent study estimated that activated sludge from global municipal WWTPs harbors 1 × 109 to 2 × 109 microbial species, the majority of which have not yet been cultivated, and 28 core taxa were identified as "most-wanted" ones (L. Wu, D. Ning, B. Zhang, Y. Li, et al., Nat Microbiol 4:1183-1195, 2019, https://doi.org/10.1038/s41564-019-0426-5). Cultivation and characterization of the "most-wanted" core bacteria are critical to understand their genetic, physiological, phylogenetic, and ecological traits, as well as to improve the performance of WWTPs. In this study, we isolated a bacterial strain, designated SJ-1, that represents a novel cluster within Betaproteobacteria and corresponds to OTU_16 within the 28 core taxa in the "most-wanted" list. Strain SJ-1 was identified and nominated as Casimicrobium huifangae gen. nov., sp. nov., of a novel family, Casimicrobiaceae. C. huifangae is ubiquitously distributed and is metabolically versatile. In addition to mineralizing various carbon sources (including carbohydrates, aromatic compounds, and short-chain fatty acids), C. huifangae is capable of nitrate reduction and phosphorus accumulation. The population of C. huifangae accounted for more than 1% of the bacterial population of the activated sludge microbiome from the Qinghe WWTP, which showed seasonal dynamic changes. Cooccurrence analysis suggested that C. huifangae was an important module hub in the bacterial network of Qinghe WWTP.IMPORTANCE The activated sludge process is the most widely applied biotechnology and is one of the best ecosystems to address microbial ecological principles. Yet, the cultivation of core bacteria and the exploration of their physiology and ecology are limited. In this study, the core and novel bacterial taxon C. huifangae was cultivated and characterized. This study revealed that C. huifangae functioned as an important module hub in the activated sludge microbiome, and it potentially plays an important role in municipal wastewater treatment plants.

Wire-drawing process with graphite lubricant as an industrializable approach to prepare graphite coated stainless-steel anode for bioelectrochemical systems.

Carbon coated stainless-steel (SS) electrode has been suggested to be a powerful composite electrode with high conductivity, excellent biocompatibility and good mechanical strength, which is promising for scaling up the bioelectrochemical systems (BESs). However, the already reported carbon coating methods were independent on the production of SS material. Additional steps and investment of equipment for carbon coating are costly, and the industrialization of these carbon coating processes remains challenging. In this study, we report an industrializable carbon coating approach that was embedded into the production line of the SS wire, which was realized through a wire-drawing process with graphite emulsion as the lubricant and carbon source. We found the slide of SS wire through the dies was essential for the graphite coating in terms of loading amount and stability. When the graphite coated SS wire was prepared as the anode and operated in a BESs, the current density reached 1.761 ± 0.231 mA cm-2, which was 20 times higher than that without graphite coating. Biomass analysis was then conducted, confirming the superior bioelectrochemical performance was attributed to the improvement of biocompatibility by the graphite coating layer. Furthermore, graphite coating by the wire-drawing process was systematically compared with the existing methods, which showed a comparable or even better bioelectrochemical performance but with extremely low cost (0.036 $·m-2) and seconds level of the time consumption. Overall, this study offers a cost-effective and industrializable approach to preparing graphite coated SS electrode, which may open up great opportunities to promote the development of BESs at large scale.

Insights into palladium nanoparticles produced by Shewanella oneidensis MR-1: Roles of NADH dehydrogenases and hydrogenases.

Biologically synthesized palladium nanoparticles (bio-Pd) have attracted considerable interest as promising green catalysts for environmental remediation. However, the mechanisms by which microorganisms produce bio-Pd remain unclear. In the present study, we investigated the roles of Shewanella oneidensis MR-1 and its NADH dehydrogenases and hydrogenases (HydA and HyaB) in bio-Pd production using formate as the electron donor. The roles of NADH dehydrogenases and hydrogenases were studied by inhibiting NADH dehydrogenases and using hydrogenase mutants (ΔhydA, ΔhyaB, and ΔhydAΔhyaB), respectively. The results showed ~97% reduction of palladium by S. oneidensis MR-1 after 24 h using 250 µM palladium and 500 µM formate. Electron microscopy images showed the presence of bio-Pd on both the outer and cytoplasmic membranes of S. oneidensis MR-1. However, the inhibition of NADH dehydrogenases in S. oneidensis MR-1 resulted in only ~61% reduction of palladium after 24 h, and bio-Pd were not found on the outer membrane. The mutants lacking one or two hydrogenases removed 91-96% of palladium ions after 24 h and showed more cytoplasmic bio-Pd but less periplasmic bio-Pd. To the best of our knowledge, this is the first study to demonstrate the role of NADH dehydrogenases of S. oneidensis MR-1 in the formation of bio-Pd on the outer membrane. It also demonstrates that the hydrogenases (especially HyaB) of S. oneidensis MR-1 contribute to the formation of bio-Pd in the periplasmic space. This study provides mechanistic insights into the production of biogenic metal nanoparticles towards their possible use in industrial and environmental applications.

Perylene pigment wastewater treatment by fenton-enhanced biological process.

Polycyclic aromatic hydrocarbons (PAHs) are regarded as priority pollutants owing to their toxic, mutagenic and carcinogenic characteristics. Perylene is a kind of 5-ring PAH with biological toxicity, and classified as a class III carcinogen by the World Health Organization (WHO). Nowadays, some of its derivatives are often used as industrial pigments. Hence, urgent attention is highly needed to develop new and improved techniques for PAHs and their derivatives removal from the environment. In this study, Fenton oxidation process was hybridized with the biological (anaerobic and aerobic) treatments for the removal of perylene pigment from wastewater. The experiments were carried out by setting Fenton treatment system before and between the biological treatments. The biological results showed that COD removal efficiency reached 60% during 24 h HRT with an effluent COD concentration of 1567.78 mg/L. After the HRT increased to 48 h, the COD removal efficiency was slightly increased (67.9%). However, after combining Fenton treatment with biological treatment (Anaerobic-Fenton-Aerobic), the results revealed over 85% COD removal efficiency and the effluent concentration less than 600 mg/L which was selected as the better treatment configuration for the biological and chemical combined system. The microbial community analysis of activated sludge was carried out with high-throughput Illumina sequencing platform and results showed that Pseudomonas, Citrobacter and Methylocapsa were found to be the dominant genera detected in aerobic and anaerobic reactors. These dominant bacteria depicted that the community composition of the reactors for treating perylene pigments wastewater were similar to that of the soil contaminated by PAHs and the activated sludge from treating PAHs wastewater. Economic analysis results revealed that the reagent cost was relatively cheap, amounting to 10.64 yuan per kilogram COD. This study vividly demonstrated that combining Fenton treatment with biological treatment was efficient and cost-effective.

Shewanella oneidensis MR-1 self-assembled Pd-cells-rGO conductive composite for enhancing electrocatalysis.

Biosynthesized noble metal nanoparticles (NPs) as promising green catalysts for electrochemical application has invited a lot of attention. However, effective electron transfer between biosynthesized NPs and electrode remains a challenge due to the uncontrollable and poor conductive property of cell substrates. In this study, graphene oxide (GO) was introduced into a bio-Pd synthesis process governed by Shewanella oneidensis MR-1, which was demonstrated to be simultaneously reduced with Pd(II) and transformed to reduced GO (rGO), resulting in the formation of a Pd-cells-rGO composite. Compared to the control without rGO (Pd-cells), the electrochemical conductivity of Pd-cells-rGO composite increased from almost zero to 196 µS cm-1, indicating the rGO facilities the electron transport across the composite. Electrochemical characterizations revealed the electrochemical active surface area (ECSA) of Pd in Pd-cells-rGO was enlarged by increasing the amount of rGO in the composite, clearly indicating that the conductive network created by rGO enable the Pd NPs receive electrons from electrode and become electrochemical active. A considerable enhancement of electrocatalytic activity was further confirmed for Pd-cells-rGO as indicated by 36.7- and 17.2-fold increase (Pd-cells-rGO with Pd/GO ratio of 5/1 vs Pd-cells) of steady state current density toward hydrogen evolution and nitrobenzene reduction at -0.7 V and -0.55 V vs Ag/AgCl, respectively. We also compared the electrocatalytic performance with MWCNTs hybrids Pd-cells-CNTs. It was found that the association of Pd, cells and rGO creates an interactive and synergistic environment to allow higher conductivity and catalytic activity under the same amount of carbon nanomaterial. The strategy developed in this work activates a highly reactive NPs and proposed a designable protocol for enhancing electrocatalytic activity of biocatalysts.